The clinical profile of seasonal affective disorder (SAD), a recurring condition of winter depressions and summer remissions, which we first described over a decade ago, has by now been widely co rroborated. Likewise, light therapy, which we first found be an effective treatment for SAD, has become a mainstream psychiatric treatment. We have continued to explore aspects of the clinical profile of SAD patients (PTS) by: a) evaluating cognitive functioning; b) surveying self- reported sensitivity to environmental chemicals and comparing responses to those of other patient groups and controls; c) surveying PTS' subjective experience of our research; and, d) comparing light visor and light box effectiveness in PTS previously treated effectively with light therapy. Seven PTS who had been treated with light therapy (light box) following participation in another winter study, were randomly assigned to either further treatment with the light box or treatment with the light visor daily for one week each. Blind raters assessed mood with the Structured Interview Guide for the Hamilton Depression Rating Scale-SAD Version (SIGH-SAD). PTS were maintained on the duration of light therapy that had previously been found to be helpful, usually less than one hour twice a day. There was no difference in depressive symptoms following the week of treatment with the light visor, as compared with the light box. A second study evaluated PTS sensitivity to exposure to environmental chemicals. A standardized, self-administered questionnaire was administered to 46 PTS, 73 patients with chronic fatigue syndrome (CFS), 27 patients with obsessive compulsive disorder, 21 patients with Addison's Disease, 19 patients with Cushing's Syndrome, and 39 controls. PTS and patients with Addison's Disease and CFS, reported highest sensitivities to exposure to various environmental chemicals, and to a significantly greater degree than those in the other groups. In general, women reported greater chemical sensitivity than did men. A third study of 10 PTS and nine controls (CRTS), administered two cognitive tests in winter and again in summer: the pattern recognition task and the Stroop task. There were no differences between PTS and CRTS on either of the tasks. For the Stroop test, however, PTS and CRTS performed better in summer than in the winter. In a final study of 32 PTS who had been through a winter protocol in the Seasonal Studies Program we gave a semi-structured interview, inquiring about their experiences as research subjects. All PTS reported that the research program had helped them, citing education about their condition, light therapy and favorable personal interactions with staff as the chief beneficial aspects. Most reported at least some element of their participation as problematic, especially time demands. Most PTS stated that they would be willing to participate in future studies.